metamorphic
Kyanite (within Quartz)
Kyanite (Al2SiO5) in crystalline Quartz base (SiO2)
Hardness: 4.5-5 (along axes) to 6.5-7 (across axes); Color: Blue, bluish-gray, or green; Luster: Vitreous to pearly; Crystal structure: Triclinic; Cleavage: Perfect; Specific Gravity: 3.53-3.67
- Hardness
- 4
- Color
- Blue, bluish-gray, or green
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 4.5-5 (along axes) to 6.5-7 (across axes); Color: Blue, bluish-gray, or green; Luster: Vitreous to pearly; Crystal structure: Triclinic; Cleavage: Perfect; Specific Gravity: 3.53-3.67
Formation & geological history
Formed through the high-pressure regional metamorphism of clay-rich (pelitic) sedimentary rocks. It is a signature mineral of the blue-schist and eclogite metamorphic facies, often found in mountain-building zones.
Uses & applications
Used industrially in the manufacture of refractory products like bricks and mortars for high-heat furnaces, automotive spark plugs, and ceramics. Gem-quality specimens are used in jewelry and collected by mineral enthusiasts.
Geological facts
Kyanite is noted for its extreme anisotropy; its hardness varies significantly depending on the direction of the scratch test. It is one of three 'polymorphs' of aluminum silicate, the other two being andalusite and sillimanite.
Field identification & locations
Identify in the field by its distinct bladed crystal habit, blue-to-green coloration, and 'anisotropic' hardness. Commonly found in schist and gneiss belts in locations like North Carolina (USA), Brazil, and the Swiss Alps.
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